#include <stdio.h>

int main() {
	int N, K, tail, head;
	while (scanf("%d %d", &N, &K)) {
		int sum = 0;
		if (N == 0 && K == 0) {
			return 0;
		}
		int a[N];
		for (int j = 0; j < N; j++) {
			a[j] = 0;
		}

		for (int j = 0; j < K; j++) {
			scanf("%d %d", &tail, &head);
			a[tail - 1]++;
			a[head - 1]++;
		}
		for (int j = 0; j < N; j++) {
			if (a[j] == 0) {
				sum = -1;
				break;
			}
			if (a[j] % 2 != 0) {
				sum++;
			}
		}
		if (sum == 0) {
			printf("YES\n");
		} else if (sum == -1) {
			printf("NO\n");
		} else {
			printf("NO\n");
		}

	}
	return 0;
}